NSTextfield value doesn't update binding when set programmatically

Hi again!
Please, excuse me in advance, if it is a yet another stupid question,
but I'm completely lost once more.
I have an NSTextField with a value bound to an NSArrayController. If a
user edits the value, everything works OK. But when I try to do the
same thing programmatically with
[aTextField setValue:aString forKey:@"value"]
I get an exception:
[<NSTextField 0x802e4d0a0> setValue:forUndefinedKey:]: this class is
not key value coding-compliant for the key value.
Seems like I'm missing something…

> Please, excuse me in advance, if it is a yet another stupid
> question, but I'm completely lost once more.
> I have an NSTextField with a value bound to an NSArrayController. If
> a user edits the value, everything works OK. But when I try to do
> the same thing programmatically with
> [aTextField setValue:aString forKey:@"value"]
> I get an exception:
> [<NSTextField 0x802e4d0a0> setValue:forUndefinedKey:]: this class is
> not key value coding-compliant for the key value.
> Seems like I'm missing something…
>